1. Field
Various examples described herein relate generally to methods and devices for regulating magnetic attraction between the magnet of a motor and the base of the motor, and in particular methods and devices for regulating magnetic attraction between the magnet and the base of a Fluid Dynamic Bearing (FDB) motor.
2. Description of Related Art
Rotary motors having small or very small profiles are often used to drive electronics equipment such as media drives (e.g., disk drives). Disk drives are capable of storing large amounts of digital data in a relatively small area. Disk drives store information on one or more recording media, which conventionally take the form of circular storage disks (e.g. media) having a plurality of concentric circular recording tracks. A typical disk drive has one or more disks for storing information. This information is written to and read from the disks using read/write heads mounted on actuator arms that are moved from track to track across the surfaces of the disks by an actuator mechanism.
Generally, the disks are mounted on a spindle that is turned by a spindle motor to pass the surfaces of the disks under the read/write heads. The spindle motor generally includes a shaft and a hub, to which one or more disks are attached, and a sleeve defining a bore for the shaft. Permanent magnets attached to the hub interact with a stator winding to rotate the hub and disk. In order to facilitate rotation, one or more bearings are usually disposed between the sleeve and the shaft.
Over the years, storage density has tended to increase, and the size of the storage system has tended to decrease. This trend has lead to greater precision and lower tolerance in the manufacturing and operating of magnetic storage disks. Accordingly, the interactions between adjacent components are of increasing importance.
One typical bearing assembly used in such storage systems includes a fluid dynamic bearing system. In a fluid dynamic bearing system, a lubricating fluid such as air or liquid provides a bearing surface between a fixed member of the housing and a rotating member of the disk hub. In addition to air, typical lubricants include gas, oil, or other fluids. Fluid dynamic bearings spread the bearing surface over a large surface area, as opposed to a ball bearing assembly, which comprises a series of point interfaces. This is desirable because the increased bearing surface reduces wobble or runout between the rotating and fixed members. Further, the use of fluid in the interface area imparts damping effects to the bearing, which helps reduce non-repeatable run-out.
Many fluid dynamic bearing motors, such as those used in hard disc drives, are subject to very limited space considerations. Thus, the magnet and the base of the motor may be positioned in relatively close proximity. When the base enclosure is made of a magnetically attractive material (e.g., a material that is magnetically permeable), this close proximity can result in attractive forces that may disrupt the smooth operation of the motor. For example, the magnetic attraction between the magnet and the base may be variable (e.g., due to variations in the distance between the base and the magnet) or it may be too powerful of an attractive force. In many motors the attractive force between the magnet and the base may also be used to preload a fluid dynamic thrust bearing, or any other thrust bearing (e.g., hydraulic, hydrostatic, spherical, conical, etc.). Thus, the magnetic force may be used to help keep the rotating portion of the motor balanced and positioned by regulating the motor bearings between the rotating region and the fixed region of the motor. Maintaining this bearing gap without excessive variation may be critical to the power, stiffness and reliability of the motor.
Accordingly, there is a need for devices, methods and systems for regulating the magnetic attraction between the motor magnet and the base region of the motor.